Australian cricketer, one of the finest leg-spin bowlers of the 20th century, taking 774 wickets in his career of first-class cricket (1927–46), including 144 wickets in 27 Test (international) matches.

The son of a schoolteacher, O'Reilly grew up in isolated rural areas, which hindered his development as a cricketer. He was unable to play regularly for New South Wales until the 1930s. A powerful man with a formidable googly, he was called up to bowl in his first Test match against South Africa (1931–32). Thereafter he was never dropped from the side, and in 19 Tests against England he captured 102 wickets. After World War II he appeared in his last Test, taking 8 for 33 against New Zealand. He retired to become a cricket columnist for the Sydney Morning Herald. O'Reilly was made Officer of the Order of the British Empire in 1971.